(1) Field of the Invention
The present invention relates to an ultrasonic diagnostic device and an image processing device, and particularly to a technique to extract a contour of an object that is subject to an examination from an image.
(2) Description of Prior Art
An ultrasonic diagnostic device receives an echo which is obtained when ultrasound emitted from an ultrasonic probe is partially reflected on reflection points and surfaces of tissue of an object of a living body that is subject to an examination. The ultrasonic diagnostic device then performs signal processing for the received echo, and generates an ultrasound image (an echo image) for the examined object. Since the ultrasonic diagnostic device generates a two-dimensional (2D) ultrasound image of an examined object of a soft part and the like without invasion, the ultrasonic device is widely used as a device which offers a high level of safety and is essential in fields such as clinical medicine.
As ultrasonic diagnostic devices are increasingly in widespread use and digitized, calculating a quantitative size, such as an area, a volume, and a change in quantity, concerning a fetus, an internal organ, and a circulatory organ has become highly important as a part of screening by the use of an ultrasonic diagnostic device. For such quantitative analysis, it is necessary to accurately extract a contour (i.e., boundary) of an object to be examined, and a variety of techniques have been developed to achieve such extraction.
For instance, Japanese Laid-Open Patent Application No. H11-164834 discloses an ultrasonic image diagnostic device, for which an operator roughly traces a boundary of tissue subject to examination so that the boundary is extracted without the effects of noise.
Japanese Laid-Open Patent Application No. H09-84739 discloses an ultrasonic image processing device. This image processing device refers to textures of images, and tissue to be examined and another tissue around the tissue to be examined are analyzed by using a plurality of learning windows. Based on difference in characteristic quantity distribution between the two pieces of tissues, a boundary of the tissue subject to the examination is extracted.
Japanese Laid-Open Patent Application No. H07-246207 also discloses an ultrasonic image processing device, which extracts a contour of tissue in accordance with a plurality of sample points that are set on a boundary of the tissue.
Japanese Laid-Open Patent Application No. H04-279156 discloses an ultrasonic three-dimensional (3D) image displaying device. This 3D image displaying device compares predetermined conditions and threshold values set by an operator with those of echo data representing shades of an image, and extracts echo data corresponding to a surface of an object to be examined.
The above conventional techniques, however, have a drawback in that they require an operator to perform a number of operations and instructions, or they cannot perform a sufficiently accurate extraction of a contour of an object.
More specifically, the above ultrasonic image diagnostic device disclosed by Japanese Patent Application No. H11-164834 first requires the operator to input a guide boundary by roughly tracing tissue subject to examination with a mouse. Secondly, the operator needs to set a starting point that is used for extracting the boundary. From this starting point, scanning lines radially extend. Then the operator also needs to manually set a detection region whose center is an intersection point of each scanning line and the boundary. After this, the image diagnostic device processes ultrasound image data within the detection region to convert it into a binary ultrasound image, and detects a boundary position for which correction is necessary. The operator is then required again to manually set the boundary.
The above ultrasonic image processing device of Japanese Patent Application No. H09-84739 requires the operator to designate each learning window with a mouse or the like. The operator needs to perform this window setting while checking learning effects, and so this is an intricate operation. Moreover, the operator needs to pay close attention to selections of the learning window's position and size so as to allow the learning process to be effectively performed.
For the conventional ultrasonic image processing device of Japanese Patent Application No. H07-246207, the operator needs to set a plurality of sample points on a boundary of an object such as a tissue to be examined. A contour obtained under this method significantly varies according to which sample points are selected, and therefore setting such accurate sample points requires as much labor and time as is required to manually trace a contour. In addition, when calculations are repeatedly performed on the same image data, this image processing device cannot always extract the same contour without the operator selecting exactly the same sample points each time even if he has set them by taking into the account the tremendous amount of care and precision that is required by the manual tracing.
The above ultrasonic 3D image displaying device disclosed by Japanese Patent Application No. H04-279156 also requires an operator's operations such as for setting predetermined conditions and threshold values, but the image displaying device may call for less operator involvement than other techniques. This image displaying device, however, is susceptible to noise in an image because it extracts a contour by simply converting density information for an ultrasound image into a binary representation. This may result in extracting an incorrect contour of tissue and a part that is subject to examination.